1. Field of the Invention
The present invention relates to a belt conveyance apparatus which regulates a deviation of a belt member during rotation thereof and an image heating apparatus which heats a recording material which carries a toner image while the recording material is pinched in a nip portion and conveyed by a belt.
2. Description of the Related Art
An image forming apparatus such as an electrophotographic apparatus or electrostatic recording apparatus forms an image by forming a toner image on a sheet, and heating and pressurizing the toner image to fix the image on the sheet. For such a fixing apparatus serving as an image heating apparatus, a roller fixing type is conventionally adopted, in which a pressurizing roller is in pressure contact with a fixing roller having a heater therein to form a fixing nip for fixing.
To achieve high image gloss and high-speed image formation, time that a sheet takes to pass through the nip needs to be increased and a toner needs to be sufficiently melted. However, in a case of the roller fixing type apparatus, a roller diameter must be increased to satisfy the above condition, resulting in enlarging the apparatus.
Accordingly, a belt fixing type apparatus capable of attaining a sufficient nip width (length in a sheet conveyance direction) while satisfying miniaturization and high-speed operation of the apparatus is discussed (Japanese Patent Application Laid-Open No. 2004-341346). The belt fixing type apparatus is provided with a fixing belt and a pressurizing belt facing each other and is structured to perform fixing while pinching and conveying a sheet between the both belts, so that the belt fixing type apparatus can attain a sufficiently larger nip width than the roller fixing type apparatus.
In a case of the belt fixing type apparatus, if a belt meanders, the belt may drop off the roller or the belt end portion may break. Accordingly, a fixing apparatus or a conveyance apparatus using a belt member needs to have a structure configured to regulate or correct lateral deviation (meandering) of the belt. In particular, in a system using a belt, a contact pressure between a fixing belt and a pressurizing belt often increases with recent needs of high-speed operation. Accordingly, belt deviation force also increases and belt deviation control is often used to prevent the meandering of the belt and breakage of the belt end portion.
However, in the belt fixing type apparatus, the belt needs to be rotated during a standby operation in addition to a fixing operation to keep the belt in a circumferential direction at a uniform temperature. Accordingly, the belt deviation control is required during the rotation. The belt deviation control puts a stress on the belt and may cause deformation or breakage of the belt and shorten a durability life.